No they dont. Voting anything here will never decrease your Steem Power. But however upvoting will drain your "voting power".

 Musing uses a steemit id named musing-threads to keep the answers and quetions here on that account as threads.. The questions here ar comments in  those posts. And answers are replies to those comments.

So when you upvote something in musing you are upvoting those comments or replies. And upvoting anything in steemit is upvoting as usual which drains only your voting power. It is in no way whatsoever possible that upvoting will drain your steem power.. 

Hope this satisfies your query.